An automatic document feeder (ADF) is provided on an upper surface of a main body of an image forming apparatus such as a copier or a printer, so as to automatically feed an original document sheet through a document reading region of the main body (see, for example, Patent Literatures 1 and 2). The main body includes contact glass. A main surface of the contact glass corresponds to a part of the upper surface of the main body. A part of the contact glass is used as the document reading region for reading an image from an original document sheet fed by the automatic document feeder. Alternatively, the main body includes main contact glass and sub contact glass in some cases. A main surface of the main contact glass and a main surface of the sub contact glass together correspond to a part of the upper surface of the main body, and the sub contact glass is disposed adjacent to the main contact glass. In this case, the sub contact glass is used as the document reading region for reading an image from an original document sheet fed by the automatic document feeder. The automatic document feeder is openably/closably attached to the main body so that an original document sheet can be placed on the contact glass or the main contact glass.
Besides, in the automatic document feeder, a paper feed tray attached to a housing and an exit tray provided in the housing overlap each other in the vertical direction in general, and the paper feed tray and the exit tray are connected to each other through a substantially U-shaped document conveyance path. Accordingly, the document conveyance path includes a conveyance path on the upstream side from a U-turn position for an original document sheet and a conveyance path on the downstream side from the U-turn position for the original document sheet, and the upstream conveyance path and the downstream conveyance path overlap each other in the vertical direction. An original document sheet set on the paper feed tray is fed to the document conveyance path, makes a U-turn in the middle, and then passes the document reading region of the main body to be discharged onto the exit tray.
Besides, the housing of the automatic document feeder includes a cover (a top cover) for unjamming processing in many cases, and when the top cover is opened, the upstream conveyance path is exposed outside. Furthermore, the top cover rotatably supports one roller of a conveyance roller pair provided in the upstream conveyance path in some cases. In such cases, when the top cover is opened, a contact between the two rollers of the conveyance roller pair provided in the upstream conveyance path is released. Accordingly, if an original document sheet is jammed in the automatic document feeder, a user can release nip (pinch with pressure) of the conveyance roller pair of the upstream conveyance path by opening the top cover, so as to remove the original document sheet from the automatic document feeder (the housing) by pulling the original document sheet with his/her hand.